Weldclass WeldForce WF-200MST, Operating Instructions Manual

Page: 21 / 36

21
Arc Length
The securing of an arc length necessary to produce
a neat weld soon becomes almost automatic. You
will find that a long arc produces more heat.
A very long arc produces a crackling or spluttering
noise and the weld metal comes across in large,
irregular blobs. The weld bead is flattened and
spatter increases. A short arc is essential if a high
quality weld is to be obtained although if it is too
short there is the danger of it being blanketed by
slag and the electrode tip being solidified in. If this
should happen, give the electrode a quick twist
back over the weld to detach it. Contact or “touch-
weld” electrodes such as E7014 Stick electrodes
do not stick in this way, and make welding much
easier.
Rate of Travel
After the arc is struck, your next concern is to
maintain it, and this requires moving the electrode
tip towards the molten pool at the same rate as it is
melting away. At the same time, the electrode has
to move along the plate to form a bead.
The electrode is directed at the weld pool at about
20º from the vertical. The rate of travel has to be
adjusted so that a well-formed bead is produced.
If the travel is too fast, the bead will be narrow and
strung out and may even be broken up into
individual globules. If the travel is too slow, the
weld metal piles up and the bead will be too large.
Making Welded Joints
Having attained some skill in the handling of an
electrode, you will be ready to go on to make up
welded joints.
A. Butt Welds
Set up two plates with their edges parallel, as
shown in Figure 1-21, allowing 1.6mm to 2.4mm
gap between them and tack weld at both ends. This
is to prevent contraction stresses from the cooling
weld metal pulling the plates out of alignment.
Plates thicker than 6.0mm should have their mating
edges bevelled to form a 70º to 90º included angle.
This allows full penetration of the weld metal to
the root. Using a 3.2mm E7014 Stick electrode
at 100 amps, deposit a run of weld metal on the
bottom of the joint.
Do not weave the electrode, but maintain a steady
rate of travel along the joint sufficient to produce a
well-formed bead. At first you may notice a
tendency for undercut to form, but keeping the arc
length short, the angle of the electrode at about
20º from vertical, and the rate of travel not too fast,
will help eliminate this.
The electrode needs to be moved along fast
enough to prevent the slag pool from getting
ahead of the arc. To complete the joint in thin
plate, turn the job over, clean the slag out of the
back and deposit a similar weld.
the electrode slowly along as it melts down.
Another difficulty you may meet is the tendency,
after the arc is struck, to withdraw the electrode so
far that the arc is broken again. A little practice will
soon remedy both of these faults.
20
o
1.6mm (1/16”)
Striking an Arc
(Fig 1-20)
Tack Weld
Butt Weld
(Fig 1-21)
Electrode
20
o
- 30
o
Tack Weld
Weld Build Up Sequence
(Fig 1-22)